The present invention relates to an exhaust gas manifold for a multi-cylinder engine, which passes the exhaust gas of several cylinders to a common outlet, and is made without any weld seam, in that it is formed from a tube piece with at least one neck formed in the side wall of the tube piece.
Such an exhaust gas manifold is disclosed in the Japanese patent application 62-206216. In this known exhaust gas manifold, two necks are formed in the side wall of a straight tube piece; these necks, after having been provided with openings, serve as exhaust gas inlets of the exhaust gas manifold. One of the two open ends serves as the outlet of the exhaust gas manifold.
In this exhaust gas manifold, it has proven to be a disadvantage that it is only suitable for bringing together the exhaust gas of adjacent cylinders. It is unsuitable, for example, for bringing together the exhaust gas of cylinders 1 and 4 of a four-cylinder in-line engine, as is desirable for high-performance engines, to increase their performance; this is because it would not be possible to install a second exhaust gas manifold which brings together the exhaust gas of cylinders 2 and 3.
Furthermore, other tube junctions formed in the most varied ways are also known. For example, the German utility model 9100867 describes a tube junction in which two tube segments which have been flattened on one side at the end and which rest against each other are inserted into a larger tube. In the tube junction known from the European patent application 192995, a main tube has an incision into which the end of another tube segment, which is formed accordingly, opens; the tube segment is connected with the main tube by welding. The German Offenlegungschrift 4228372 describes a tube junction in which a tube segment is inserted, at its end, into a neck which is mechanically produced in a tube elbow. In all three known tube junctions, it is a disadvantage that they are composed of two or three separate parts. This results in significant production costs. One of the reasons these costs are so high is that the parts to be connected with each other must fit precisely relative to one another, and must be aligned correctly with one another, so that sufficient mechanical strength and a leak-proof seal of the tube junction is guaranteed.
In exhaust gas manifolds known from car racing, which are formed as a tube junction, a hole is cut in the outside wall of a pre-bent tube, generally using a laser cutter, and a correspondingly adapted tube is welded into it. Such tube junctions suffer from the same disadvantages as those described above.
Tube junctions produced from two half shells are also expensive to produce, because of the long weld seams which connect the two half shells with each other.
Another tube junction is described in the German patent 4103083. This known tube junction proceeds from a tube piece which has been hydrostatically transformed, especially widened, and subsequently been converted to a double tube in certain regions, by being indented. In this known tube junction it is disadvantageous that the arrangement of the two inlets cannot be freely selected; instead, the two inlets are always very closely adjacent.
In the article "Hydrostatic forming of tubing produces complex parts" (57 Automation 10 (1963.06) p. 85/85), the method of hydrostatic forming is explained in connection with different hollow elements, and the formation of a neck in the wall of a bent tube piece is also presented.